1. Field of the Invention
The present invention relates to an organic electro luminescence display device, and more particularly to an organic electro luminescence display device that is adaptive for improving rigidity.
2. Description of the Related Art
Recently, there have been developed a variety of flat panel display devices that can reduce their weight and size, which are a disadvantage of a cathode ray tube CRT. The flat panel display device includes a liquid crystal display LCD, a field emission display FED, a plasma display panel PDP and an electro luminescence EL display device. Particularly, the EL display device has electrodes stuck to both of the sides of an organic light emitting layer basically composed of a hole transport layer, a light emitting layer and an electron transport layer, and becomes the center of attention as a next generation flat panel display device because of its characteristics such as wide viewing angle, high aperture ratio and high chromaticity.
The EL display device is largely divided into an inorganic EL display device and an organic EL display device in accordance with a material used. In the organic EL display device, electrons and holes form a pair and then become extinct to emit light if electric charges are injected into an organic EL layer which is formed between a hole injection electrode and an electron injection electrode, thus there is an advantage in that it can be driven at a lower voltage than the inorganic EL display device. Further, the organic EL display device can be driven at a low voltage of not greater than 10V in comparison with the PDP or the inorganic ELD as well as forming the device on a flexible transparent substrate like plastics, and its power consumption is relative low and its color impression is excellent.
FIG. 1 is a sectional diagram briefly representing a related art organic EL display device, and FIG. 2 is a diagram for explaining a light emitting principle of the organic EL display device shown in FIG. 1.
The organic EL display device shown in FIG. 1 includes an organic EL array 15 having a first electrode (or an anode electrode) 4 and a second electrode (or a cathode electrode) 12 formed on a substrate 2 to cross each other with an organic light emitting layer 10 therebetween; and a cap 28 for packing the organic EL array 15.
A plurality of anode electrodes 4 of the organic EL array 15 is formed on the substrate 2 to be separate from one another with a designated distance therebetween. An insulating film 6 having a hollow part for each EL cell (EL) area is formed on the substrate 2 where the anode electrode 4 is formed. A barrier rib 8 is located on the insulating film 6, wherein the barrier rib separates an organic light emitting layer 10 and the cathode electrode 12 which are to be formed on the insulating film 6. The barrier rib 8 is formed in a direction of traversing the anode electrode 4 and has a reverse taper structure that an upper part has a wider width than a lower part. The organic light emitting layer 10 and the cathode electrode 12 composed of an organic compound are sequentially deposited on the whole surface of the insulating film where the barrier rib 8 is formed. The organic light emitting layer 10 includes an electron injection layer, an electron transport layer, alight emitting layer, a hole transport layer, and a hole injection layer.
The organic EL array 15 has characteristics of being easily deteriorated by moisture and oxygen. In order to solve this problem, there is performed an encapsulation process that the cap 28 and the substrate 2 where the organic EL array 15 is formed are bonded through a sealant 25 such as epoxy resin, thus the organic EL array 15 is protected from the moisture and oxygen.
The cap 28 includes a getter 22 which is located on a surface opposite to the organic EL array 15 and absorbs moisture and oxygen. Herein, the getter 22 is of an inorganic oxide, i.e., calcium oxide CaO and barium oxide BaO which form an oxalic radical (OH) by reacting on moisture.
In the organic EL display device, as shown in FIG. 2, if a voltage is applied between the anode electrode 4 and the cathode electrode 12, the electron generated at the cathode electrode 12 moves to the light emitting layer 10C through an electron injection layer 10a and an electron transport layer 10b. Further, the hole generated at the anode electrode 4 moves to the light emitting layer 10c through a hole injection layer 10e and a hole transport layer 10d. Accordingly, in the light emitting layer 10c, the electron and the hole supplied from the electron transport layer 10b and the hole transport layer 10d are recombined to form an exiton, and the exiton is excited again to a ground state, thus a light of a fixed energy is emitted to the outside through the anode electrode 4, thereby displaying a picture.
On the other hand, the related art cap 28 is formed in a three step structure where it includes a first plane 28a where the getter 22 is formed, a third plane 28c over which the sealant 25 is spread, and a second plane 28b between the first plane 28a and the third plane 28c, thus there is a problem in that the size of the overall organic EL display device is big. In order to solve the problem, there is proposed a cap 29 of a two step structure shown in FIG. 3.
The cap 29 shown in FIG. 3 includes a first plane 29a where the getter 22 is located, a second plane 29b over which the sealant 25 is spread, and a vertical plane 29c between the first plane 29a and the second plane 29b, thus the device can be made thinner than the cap 28 of the three step structure shown in FIG. 1.
However, the structure shown in FIG. 3 has an advantage of being made thinner, but there is a problem in that it can be twisted by a small mechanical impact, shock and soon because rigidity is deteriorated.